Nowadays, shredders are widely used to cut sheet-like articles. If a relatively thick article whose thickness is beyond an acceptable range (for example a thick paper or a compact disc) is shredded by a shredder, the thick article is readily jammed. Under this circumstance, the shredder has a usage problem or even a breakdown. For avoiding the occurrence of the jamming problem, a thickness detecting mechanism is often mounted in the shredder to determine whether the article to be shredded is beyond the acceptable range.
FIG. 1 is a schematic perspective view illustrating a portion of a shredder having a thickness detecting mechanism according to the prior art. The shredder 1 includes an entrance 11, a shredding path 12, a sustaining element 13, a thickness sensing module 14, a driving motor 15, a transmission gear set 16 and a shredding knife assembly 17. The entrance 11 is disposed above the shredding path 12. The sustaining element 13 is arranged at a side of the shredding path 12. The thickness sensing module 14 is disposed behind the sustaining element 13. As shown in FIG. 1, the thickness sensing module 14 includes a light emitter 141 and a light receiver 142, which are arranged behind the sustaining element 13. The thickness sensing module 14 and the sustaining element 13 are collectively referred as a thickness detecting mechanism. The shredding knife assembly 17 is disposed at the outlet of the shredding path 12. The transmission gear set 16 is interconnected between the shredding knife assembly 17 and the driving motor 15, and engaged with the shredding knife assembly 17 and the driving motor 15. As a consequence, the shredding knife assembly 17 could be driven by the driving motor 15 to implement a shredding operation.
Hereinafter, the operations of the shredder 1 will be illustrated in more details with reference to FIG. 1. First of all, an article to be shredded (not shown) is fed into the shredding path 12 through the entrance 11. When the article is contacted with and sustained against the sustaining element 13, the sustaining element 13 is shifted backwardly to result in a shift distance with respect to its original place. In the thickness sensing module 14, the light emitter 141 continuously emits the sensing light and the sensing light is received by the light receiver 142. In a case that the sustaining element 13 fails to completely shelter the sensing light, the article is permitted to feed through the shredding path 12 so as to perform a shredding operation. Whereas, if the sensing light is completely sheltered by the sustaining element 13, the shredding operation of the shredder 1 is interrupted.
That is, in the case that the shift distance of the sustaining element 13 is not sufficient to completely shelter the sensing light emitted from the light emitter 141, it is meant that the thickness of the article is accepted by the shredder 1. Under this circumstance, the article is continuously advanced in the shredding path 12. In addition, the shredder 1 has a shredding sensor (not shown) under the sustaining element 13. When the advancing article approaches the shredding knife assembly 17, the shredding sensor will detect the presence of the article. Meanwhile, the driving motor 105 and the transmission gear set 16 that is driven by the driving motor 105 begin to rotate. Upon rotation of the transmission gear set 16, the shredding knife assembly 17 is driven to implement a shredding operation.
As previously described, by using the sustaining element 13 and the thickness sensing module 14, the usage status of the shredder 1 may be determined according to the thickness of the article to be shredded. In other words, the sustaining element 13 and the thickness sensing module 14 are advantageous of avoiding the problem of causing jammed paper so as to extend the operating life of the shredder 1.
Nowadays, with increasing awareness of environmental protection, more and more electrical apparatuses are designed in views of power-saving concepts. The conventional shredder 1, however, still has no power-saving mechanism. For example, if a five-sheet article within the acceptable thickness range is fed into the shredding path 12, the driving motor 15 of the shredder 1 is operated at a fixed rotating speed to provide a constant torsion force to the shredding knife assembly 107. As such, the five-sheet article is shredded by the shredding knife assembly 107 with the constant torsion force. Whereas, if a two-sheet article is fed into the shredding path 12, the driving motor 15 of the shredder 1 is also operated in the fixed rotating speed to provide the constant torsion force to the shredding knife assembly 107. As such, the two-sheet article is shredded by the shredding knife assembly 107 with the constant torsion force. Since a constant torsion force is used to shred the article regardless of the sheet number of the article fed into the shredding path 12, the conventional shredder 1 may consume much power after a long-term use period. Therefore, there is a need of providing a power-saving shredder in order to obviate the problems encountered from the prior art.